If i switch to mb_chars, like you do in irb-example on starting with 16.9 i got no errors with the following code:
`
7 <td><%= h person.name %></td>
8 <td><%= person.name.length %></td>
9 <td><%= person.name.mb_chars.length %></td>
10 <td><%=h person.name.mb_chars.reverse %></td>
`

whats the difference between mb_chars and chars?
The funny thing: there is none. But why the hell i got a Enumable as return?

# File activesupport/lib/active_support/core_ext/string/multibyte.rb, line 57
def chars
ActiveSupport::Deprecation.warn('String#chars has been deprecated in favor of String#mb_chars.', caller)
mb_chars
end

Using the example-setup from the book to confirm the correctness of all examples:
Rails 2.2.2
Ruby 1.8
Gems: 1.3.1